An example of a conventional vibrating gyroscope is illustrated in FIG. 13. In this vibrating gyroscope, the vibrator 4 has piezo-electric elements 2 and 3 which are respectively connected via the respective impedance elements Z1 and Z2 to the output side of drive apparatus 6. The output side of this drive apparatus 6 is connected via another impedance element Z3 to capacitor element C. Therefore, drive signals from the drive apparatus 6 are simultaneously applied to the piezo-electric elements 2 and 3 and to capacitor element C.
The outputs at the respective nodes of the impedance elements Z1 and Z2 and the piezo-electric elements 2 and 3 are combined. This combined output and the output at the node of impedance element Z3 and capacitor element C are supplied to differential amplifier 7. The output from the differential amplifier 7 is fed back to the drive apparatus 6 so that the vibrator 4 is self-vibrating. Additionally, the outputs at the respective nodes of impedance elements Z1 and Z2 and piezo-electric elements 2 and 3 are supplied to another differential amplifier 8, so as to obtain an angular velocity detection signal based on the output from differential amplifier 8.
An example of a vibrator 4, shown in FIG. 14, has a square cross-sectional shape and has piezo-electric element 2 on one side surface 1a of vibration member 1 having a resonance point and piezo-electric element 3 on another side surface 1b adjoining side surface 1a. Another example of a vibrator 4, shown in FIG. 15, has piezo-electric elements 2 and 3 split in the wide direction on the same side of vibration member 1. Another example of a vibrator 4, shown in FIG. 16, has piezo-electric elements 2 and 3 on opposite sides of vibration member 1. Another example of a vibrator 4, shown in FIG. 17, has the respective piezo-electric elements 2a and 2b on opposite side surfaces of vibration member 1 and connects them in parallel so that they act essentially as one piezo-electric element 2, and has respective piezo-electric elements 3a and 3b on the other opposite sides and connects them in parallel so that they act essentially as one piezo-electric element 3.
Still another example of a vibrator 4, shown in FIG. 18, has a triangular cross-sectional shape and has piezo-electric elements 2 and 3 on two side surfaces of vibration member 1 having a resonance point. Another example of a vibrator 4, shown in FIG. 19, has a circular cross-sectional shape and has piezo-electric elements 2 and 3 on the peripheral surface of vibrator member 1 having a resonance point. Thus, in all these examples, at least two piezo-electric elements are formed on the side surfaces of vibration members having various sectional shapes. FIG. 20 shows an equivalent circuit for a single piezo-electric element for the vibrators shown in FIGS. 14 to 19, which is represented as a parallel resonance circuit with damping capacity Cd connected in parallel to a series resonance circuit comprising an inductor L1, a capacitor C1 and a resistance R1. Further, the vibrators comprising two piezo-electric elements 2 and 3 in vibration member 1 are represented equivalently in FIG. 21.
The conventional vibration gyroscope shown in FIG. 13 applies the drive signals from drive apparatus 6 to piezo-electric elements 2 and 3 via impedance elements Z1 and Z2. This causes the signal applied to piezo-electric elements 2 and 3 to decrease when the impedances of piezo-electric elements 2 and 3 drop in the vicinity of mechanical series resonance frequency f.sub.s in vibrator 4. The frequency at which the output from differential amplifier 7 is maximized and the mechanical series resonance frequency f.sub.s do not coincide.
In order to overcome such problems, the present applicant has already proposed, in Japanese Patent Application Hei 6-2364 and Japanese Patent Application Hei 6-10348, a vibration control apparatus that can impart self-induced vibration by stabilizing the vibrator at a frequency set to the mechanical series resonance frequency f.sub.s of the vibrator. In other words, the vibrator oscillates at or near its resonant frequency. When used with a vibrating gyroscope, the apparatus can also effectively decrease formation of low voltage and variations in voltage.
FIG. 22 illustrates an example of a vibration control apparatus in the above patent applications of the applicant. This vibration control apparatus is one that controls vibrations in a vibrator 4, as shown in FIGS. 14 through 19. As discussed above, such a vibrator 4 comprises at least one pair of piezo-electric elements 2 and 3 on the side surfaces of vibration members 1 having varying cross-sectional shapes and resonance points. Signal output terminal 9 of drive apparatus 6 is respectively connected to signal input terminals 11L and 11R of feedback amplifier 10L having feedback resistance R.sub.fL and feedback amplifier 10R having feedback resistance R.sub.fR. Feedback input terminals 12L and 12R of the feedback amplifiers 10L and 10R are respectively connected to one of the electrodes of piezo-electric elements 2 and 3, so as to apply the drive signal to the vibrator. The other electrodes of piezo-electric elements 2 and 3 are connected via capacitor Cc to compensation signal output terminal 13 of drive apparatus 6 which outputs a compensation signal for the damping capacity of vibrator 4, so that the compensation signal is combined with signals of the other electrodes of piezo-electric elements 2 and 3. This combined output signal is amplified by integrating amplifier 17. The signal output terminal 18 is connected to the input terminal 14 of the drive apparatus 6, so that the vibrator 4 is given self-induced vibration.
The output of integrating amplifier 17 and the drive signal at signal output terminal 9 are supplied to the differential amplifier 22 and differentially amplified. The output of the differential amplifier 22 is supplied via variable resistance VR to feedback input terminals 12L and 12R of feedback amplifiers 10L and 10R supply current at these input terminals. The currents vary depending on the current values flowing in the equivalent resistances of piezo-electric elements 2 and 3, i.e., depending on the temperature dependencies. The outputs of the feedback amplifiers 10L and 10R are supplied to differential amplifier 20, so that the Coriolis force arising from the angular velocity acting on vibrator 4 can be detected as voltage. Further, the respective feedback resistances Rf.sub.L and Rf.sub.R are connected between the output sides of feedback amplifiers 10L and 10R and the corresponding feedback input terminals 12L and 12R sides.
FIG. 23 illustrates an example of the drive apparatus 6 having the compensation signal output terminal 13 as shown in FIG. 22. This drive apparatus 6 has a non-inverting amplifier 15 and an inverting amplifier 16. The signal from input terminal 14 is amplified at the non-inverting amplifier 15. The output from the non-inverting amplifier 15 is amplified at inverting amplifier 16 and then supplied to signal output terminal 9 as the drive signal. The output from the non-inverting amplifier 15 is also supplied to the signal output terminal 9 as a compensation signal. The drive signal and the compensation signal have a phase difference of 180.degree.. The amplitude ratios of these signals are appropriately set by inverting amplifier 16.
With the vibration control apparatus illustrated in FIG. 22, the imaginary parts of the current flowing in piezo-electric elements 2 and 3, relative to the damping capacities Cd, are extinguished by the combined compensation signal via capacitor Cc. Therefore, the output of integrating amplifier 17 becomes only the real part of the current flowing in piezo-electric elements 2 and 3. Consequently, the voltage gain of integrating amplifier 17 maximizes at the mechanical series resonance frequency f.sub.s of vibrator 4, thereby, making it possible to impart self-induced vibration by stabilizing vibrator 4 at a frequency in accurate agreement with the mechanical series resonance frequency f.sub.s. In other words, the vibrator oscillates at or near its resonant frequency. Also, the self-induced vibration at mechanical series resonance frequency f.sub.s uses a capacitor Cc having a temperature dependence corresponding to the temperature dependence of damping capacities Cd of vibrator 4, so that further stabilization becomes possible.
As described above, the self-induced vibration is provided by at least one pair of piezo-electric elements without providing an independent piezo-electric element to obtain feedback output. Therefore, fluctuations in amplitude that accompany characteristic differences in the piezo-electric elements themselves will not occur, as in cases where a feedback piezo-electric element for self-induced vibration is furnished .separately from the drive piezo-electric element. However, the currents flowing through the pair of feedback piezo-electric elements 2 and 3 that form the vibrator 4 are determined by the impedance of vibrator 41 Therefore, when the equivalent resistances and damping capacity of the vibrator 4 change due to ambient temperature, the currents change also.
With the above vibration control apparatus, fluctuations in damping capacity due to temperature changes are compensated for by capacitor Cc. Fluctuations or variations in equivalent resistances due to temperature changes are compensated for by supplying the output of differential amplifier 22 to feedback input terminals 12L and 12R of feedback amplifiers 10L and 1OR via variable resistance VR. However, there is no control over the temperature changes in the combined currents flowing through piezo-electric elements 2 and 3. It is also difficult to completely compensate for these variations. Therefore, due to temperature changes, the amplitude of self-oscillating vibration in the vibrator 4 varies inversely to the equivalent resistances. The amplitude of the vibration corresponding to the input angular velocity also varies correspondingly in the direction of self-induced vibration and in the orthogonal direction, so that detection sensitivity varies and detection accuracy can end up declining.